A plank AB 3.0m long weighs 20kg and with it's centre of gravity 2.0m from the end A. it rests on two supports at C and D. i) compute the values of the reaction forces R1 and R2 at C and D . ii) how far from D and in which side of it must a mass of 24kg be placed on the plane so as to make the reaction equal? what are their values ? iii) without this 24kg ,what vertical force applied at B will just lift the plank clear of D ? what is then the reaction at C